Modern computing systems include one or more processors that are coupled to a system memory over a memory bus. The system memory includes memory locations that are addressable by the processor over the memory bus. The processor reads data from and writes data to the system memory via the memory bus. The processor might typically include one or more caches for faster reads and writes of data that is available in the cache.
As the system memory may not be large enough to contain all of the data and instructions that are needed, paging algorithms have been developed to page data and instruction between an external non-volatile storage (such as a hard disk drive or solid state disk) and system memory.
Database systems often manage database tables that are quite large, and thus often the structure of such tables is persisted on external non-volatile storage, while the current data being operated upon is paged into the system memory. However, more recent database systems store database tables in volatile system memory. The durability of such in-memory tables is ensured by logging all changes to external storage such as magnetic hard disk drives or solid state drives. In addition, such database systems may also maintain checkpoints of the database state on such external storage. After a crash, the latest database state is rebuilt in system memory from the latest checkpoints and the log.